Here are a few sheets with character design studies by Tom Oreb dating back to the 1950s. Looking at the Aurora drawings I have to say that Marc Davis and Iwao Takamoto had it fairly easy when it came to finalizing the character for animation. Everything is already there in Oreb's sketches. Overall styling, line and shape language, hair and costume, all of it.
He also drew rough concepts for many characters in 101 Dalmatians. These were based on story sketches by Bill Peet, who single handedly storyboarded the entire movie.
Milt Kahl and other animators referred to these drawings while adjusting the designs slightly for final animation.
Go to Howard Lowery Auctions, where you'll find Oreb's work for sale once in a while.
Much more on Nanny's design in this previous post: